Radiation (G9-ARIS)

Two metal cans are identical, except that one has a shiny silver outer surface and the other has a dull black outer surface. They each have 300 g of water at 80 °C sealed inside them. They are both in a vacuum, in the darkness of outer space.

How does the temperature of the water in each one change?

• Neither one will cool down.

• The water in the black can cools more slowly than that in the shiny can.

• The water in the shiny can cools more slowly than that in the black can.

• They both cool down at the same rate.

Vacuum flasks usually have silvered walls that help to keep the contents of the flask hot.

Why are the walls silvered?

• to absorb thermal energy from the air around the flask

• to increase the rate of convection inside the flask

• to reduce energy loss to the surroundings by conduction

• to reflect thermal radiation back into the flask

On a cold day, a shiny metal rod feels colder to the touch than a black plastic rod.

Which statement explains this observation?

• The metal rod is a better absorber of infra-red radiation than the plastic rod.

• The metal rod is a better thermal conductor than the plastic rod.

• The metal rod is a worse absorber of infra-red radiation than the plastic rod.

• The metal rod is a worse thermal conductor than the plastic rod.

Which statement about infra-red radiation is correct?

• A black surface is a poor absorber of infra-red radiation.

• A dull surface is a better emitter of infra-red radiation than a shiny surface.

• A shiny surface is a better absorber of infra-red radiation than a dull surface.

• A white surface is a poor reflector of infra-red radiation.

Which statement about thermal radiation is correct?

• It can only occur in a vacuum.

• It involves movement of electrons through a material.

• It involves movement of atoms.

• It is infra-red radiation.

Two methods by which thermal energy can be transferred are conduction and radiation. Which statement is correct?

• Conduction involves density changes in fluids.

• Conduction only occurs in solids.

• Radiation cannot occur in a vacuum.

• Radiation involves electromagnetic waves.

What is the name of the process f heat transfer using electromagnetic waves?

• conduction

• convection

• evaporation

• radiation

The diagram shows a vacuum flask used to keep liquid hot.

How does thermal energy pass through the vacuum?

• conduction only

• convection only

• radiation

• conduction and convection

A heating engineer fits a heater to the ceiling of an office so that workers in the office are kept warm.

How does thermal energy reach the workers below the heater?

• conduction and convection

• convection and radiation

• convection only

• radiation only

The diagram shows the cross-section of a vacuum flask containing a hot liquid in a cold room.

X and Y are points on the inside surfaces of the walls of the flask.

How is thermal energy transferred between X and Y?

• by conduction and convection

• by conduction only

• by radiation and convection

• by radiation only